Currently lighting applications are dominated by incandescent lighting products. Because they use hot filaments, these products produce considerable heat, which is wasted, in addition to visible light that is desired. Halogen-based lighting enables filaments to operate at a higher temperature without premature failure, but again considerable non-visible infrared light is emitted, and this heat is directed away from the lamp to the extent feasible. This is conventionally done by using a dichroic reflector shade that preferentially passes the infrared as well as a portion of the visible light. The nature of this dichroic reflector is such that it passes several different visible colors as well as the infrared radiation, giving a somewhat pleasing appearance. This has led to numerous decorative applications for such halogen lights. These lights consume substantial current and dissipate considerable unwanted heat. Halogen bulbs are designed to operate at a variety of voltages between 12 volts (V) to as high 15 V or greater.
Light emitting diodes have operating advantages compared to ordinary incandescent and halogen lights. LEDs typically emit a narrow range of wavelengths, thereby eliminating, to a large degree, wasted non-visible energy. White light can be created by combining light colors. LEDs can also emit in the ultraviolet wavelength range, in which case white light (as well as certain colors) can be created by excitation of a phosphor.
LEDs have an extremely long life compared to incandescent and halogen bulbs. Whereas incandescent and halogen bulbs may have a life expectancy of 2000 hours before the filament fails, LEDs may last as long as 100,000 hours, and 5,000 hours is fairly typical. Moreover, unlike incandescent and halogen bulbs, LEDs are not shock-sensitive and can withstand large forces without failure, while the hot filament of an incandescent or halogen bulb is prone to rupture.
Halogen bulbs, incandescent bulbs, and LEDs all typically require a fixed operating voltage and current for optimal performance. Too high an operating voltage causes premature failure, while too low an operating voltage or current reduces light output. Also, the color of incandescent and halogen lights shifts toward the red end of the visible spectrum as current and voltage are reduced. This is in contrast to LEDs, in which only the intensity of the light is reduced. Furthermore, as the voltage to an incandescent or halogen light is reduced, its temperature drops; as a result, its internal resistance decreases, leading to higher current consumption but without commensurate light output. In cases where batteries are used as the source of energy, they can be drained without producing visible light.
Incandescent and halogen bulbs require a substantial volume of space to contain the vacuum required to prevent air from destroying the filament, to keep the glass or silica envelope from overheating, and to insulate nearby objects from the emitted heat. In contrast, LEDs, as solid-state devices, require much less space and generate much less heat. If the volume of an incandescent or halogen bulb is allocated to a solid-state LED light, considerably more functions may be incorporated into the lighting product.
Unlike incandescent and halogen lights, LEDs ordinarily produce light in a narrow, well-defined beam. While this is desirable for many applications, the broad-area illumination afforded by incandescent and halogen lights is also often preferred. This is not easily accomplished using LEDs. The light produced by incandescent and halogen lights that is not directed towards the target performs a useful function by providing ancillary illumination and a decorative function. Halogen lights with their dichroic reflectors do this necessarily, but ordinary incandescent lights can employ external shades, not part of the light bulb, in a variety of artistic designs to make use of this otherwise misdirected light.